Semiconductor devices

ABSTRACT

A device comprises a first sub-collector formed in an upper portion of a substrate and a lower portion of a first epitaxial layer and a second sub-collector formed in an upper portion of the first epitaxial layer and a lower portion of a second epitaxial layer. The device further comprises a reach-through structure connecting the first and second sub-collectors and an N− well formed in a portion of the second epitaxial layer and in contact with the second sub-collector and the reach-through structure. The device further comprises N+ diffusion regions in contact with the N− well, a P+ diffusion region in contact with the N− well, and shallow trench isolation structures between the N+ and P+ diffusion regions.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a divisional application of U.S. applicationSer. No. 12/237,148, filed on Sep. 24, 2008, which is a divisionalapplication of U.S. application Ser. No. 11/422,690, filed on Jun. 7,2006, the contents of which are incorporated by reference in itsentirety herein.

FIELD OF THE INVENTION

The invention relates generally to semiconductor devices, and morespecifically, devices with noise isolation and ESD protectioncomponents.

BACKGROUND OF THE INVENTION

Electrostatic discharge (ESD), a surge in current (negative or positive)that occurs when a large amount of current is applied to an integratedcircuit, may cause substantial damage to, or even destruction of, thecircuit. ESD events are particularly troublesome for BiCMOS RF (radiofrequency) chips because of their low power requirements and extremesensitivity. Therefore, on-chip ESD protection circuits for BiCMOS chipsare essential.

Historically, there have been several approaches to noise isolation andESD protection. These include: STI-bound P+/N− well diode structures(also known as STI-bound diodes); polysilicon MOSFET (metal oxidesemiconductor field effect transistor) gate defined PN diode structures(also known as polysilicon bound diodes); N+ in P− substrate diodes,whether with a poly border or shallow trench isolation to define theedge (also known as N− well to substrate diodes). Such approaches mayresult in (1) creating a forward-biased PNP structure and injectingcurrent into the substrate, which generates noise; (2) forming avertical PNP structure with a common collector, which may have highleakage, may cause Darlington amplification effects, or may betemperature- or photo-sensitive; or (3) non-ideal turn-on voltage.

Accordingly, a need has developed in the art for structures that willprovide noise isolation and ESD protection in RF or similarapplications.

SUMMARY OF THE INVENTION

In a first aspect of the invention, a device comprises a firstsub-collector formed in an upper portion of a substrate and a lowerportion of a first epitaxial layer and a second sub-collector formed inan upper portion of the first epitaxial layer and a lower portion of asecond epitaxial layer. The device further comprises a reach-throughstructure connecting the first and second sub-collectors and an N− wellformed in a portion of the second epitaxial layer and in contact withthe second sub-collector and the reach-through structure. The devicefurther comprises N+ diffusion regions in contact with the N− well, a P+diffusion region contained within the N− well, and shallow trenchisolation structures between the N+ and P+ diffusion regions.

In a second aspect of the invention, a device comprises a P− dopedregion located within a first epitaxial layer which is isolated by adeep trench isolation structure and a sub-collector formed in an upperportion of a substrate and a lower portion of the first epitaxial layer.The device further comprises a reach-through structure connecting thesub-collector and a first N+ diffusion region, and a second N+ diffusionregion diffused in the second epitaxial layer. The device furthercomprises a P+ diffusion region diffused in the second epitaxial layerand isolated from the N+ diffusion regions.

In another aspect of the invention, a device comprises a P− doped regionlocated within a first epitaxial layer. The device further comprises asub-collector formed in an upper portion of a substrate and a lowerportion of a first epitaxial layer and a reach-through structureconnecting the sub-collector and a first N+ diffusion region. The devicefurther comprises an N+ diffusion region connecting with the secondepitaxial layer, and a P+ diffusion region in contact with the secondepitaxial layer.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1-11 show alternative structures in accordance with the invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The invention relates to a semiconductor device. In embodiments, theinvention more specifically relates devices with noise isolation and ESDprotection components. In embodiments, a stacked reach-through structureand deep sub-collector form a cathode or collector. Alternatively, inembodiments, dual epitaxial layers form a double-epitaxy triple-well ESDnetwork. In either instance, a P-type device (e.g. a PFET) or an N-typedevice (e.g. an NFET) may be isolated from the substrate. The inventionmay be suitable for millimeter wave (mmW) technology for RF CMOS,BiCMOS, RF BiCMOS, RF BiCMOS Silicon Germanium (SiGe), and RF BiCMOSSilicon Germanium Carbon (SiGeC) devices, to name a few. (U.S. Pat. No.7,329,940 is herein incorporated by reference in its entirety.)

In the discussion that follows, like reference numerals are used torefer to similar elements, such that a detailed discussion of each likeelement is not repeated for each embodiment. Further, as will beunderstood by one of skill in the art, in alternative embodiments,although shown in the figures in only two dimensions, elements of thepresent invention may be configured in three-dimensional rings around avertical center line drawn through each figure. That is, in alternativeembodiments, all elements, some elements, or no elements may beconfigured in three-dimensional rings.

Referring to FIG. 1, a double-epitaxy, double sub-collector ESD deviceaccording to one embodiment of the invention is shown. The device may beformed by any conventional methods. The structure shown in FIG. 1comprises a substrate 10, a first epitaxial (epi) layer 12, and a secondepi layer 14. The first epi layer 12 is located between the substrate 10and the second epi 14. In one embodiment, the substrate 10 may beSilicon or Germanium, but other materials and/or substrates may equallybe used, such as for example, SOI. The thickness of the first epi layer12 may range from approximately 0.25 to 5 μm, which effectivelyincreases the distance of a sub-collector from a surface of the device.The thickness of the second epi layer 14 is, in embodiments of theinvention, approximately in the range of 0.25 to 5 μm, which may be inthe same range as the thickness of the first epi layer 12.

The structure further comprises a first sub-collector 16, also referredto as a “deep sub-collector” (DS), which is an N+ region formed in anupper portion of the substrate 10 and a lower portion of the first epilayer 12. A deep sub-collector 16 is, for example, a collector that islocated relatively further away from the top surface of the structure.In embodiments, the deep sub-collector 16 may have been formed through aconventional ion implantation process, using dopants such as, forexample, Arsenic (As), Antimony (Sb), Phosphorous (P), or other N-dopedelements. In embodiments, the doping concentration of the deepsub-collector 16 is relatively high, for example from 1×10¹⁸/cm³ to1×10²¹/cm³. In embodiments, the sheet resistance of the deepsub-collector 16 may range from approximately 1 to 100 ohms/square.

The structure further comprises a second sub-collector 18, also referredto as a “near sub-collector” (NS), which is formed in an upper portionof the first epi layer 12 and lower portion of the second epi layer 14.A near sub-collector 18 is, for example, a collector that is locatedrelatively closer to the top surface of the structure than the deepsub-collector 16. In embodiments, the near sub-collector 18 may havebeen formed through a conventional ion implantation process, usingdopants such as, for example, Arsenic (As), Antimony (Sb), Phosphorous(P), or other N-doped elements. In embodiments, the doping concentrationof the near sub-collector 18 is relatively high, for example, from1×10¹⁸/cm³ to 1×10²¹/cm³. In embodiments, the sheet resistance of thenear sub-collector 18 may range from approximately 1 to 100 ohms/square.

The structure further comprises a doped region 20, which is formed in aportion of the first epi layer 12 above the deep sub-collector 16 andbelow the near sub-collector 18. The doped region 20 may be either a P−region or an N− region. If the doped region 20 is a P− region, this maybe the natural epi doping, or may be implanted, for example, with Boron(B). If the doped region 20 is an N− region, this may be the natural epidoping, or may be implanted, for example, with Arsenic (As), Antimony(Sb), or Phosphorous (P). If the doped region 20 is an N− region, it isnot as isolated from the substrate 10 as the case where it is a P−region, but such an N− region provides a lower resistance cathode than aP− region.

The structure further comprises a deep reach-through 22, which is incontact with the lateral edges of the deep sub-collector 16 and the nearsub-collector 18, and electrically and thermally connects the twosub-collectors. In embodiments, the deep reach-through 22 may have beenformed through a conventional ion implantation process, using dopantssuch as, for example, Arsenic (As), Antimony (Sb), Phosphorous (P), orother N-doped elements. Although there is, in embodiments, a separationbetween the deep sub-collector 16 and the near sub-collector 18, thedeep reach-through 22 provides a low-resistance connection.

The structure further comprises a near reach-through 24, which is incontact with the lateral edge of the near sub-collector 18, and stackedupon the deep reach-through 22. In embodiments, the near reach-throughmay have been formed in any conventional manner, as described withreference to the deep reach-through 22.

Optionally, the structure may further comprise a deep trench isolation(DTI) structure 26 in contact with the lateral edge of the stackedreach-throughs 22 and 24. It should be understood that the DTI 26 mayinclude dielectric sidewall material and a fill material in thedielectric, e.g. polysilicon, BPSG, or PSG. Alternatively, the DTI 26may comprise local oxidation of Silicon (“LOCOS”) or recessed oxidestructures (“ROX”) structures. The DTI 26 is integrated with both thedeep and near reach-through structures 22 and 24. In the case where theDTI 26 is not included in the structure, it will be understood that thedeep and near reach-throughs 22 and 24 function as a perimeter aroundthe first and second epi layers.

The structure further comprises an N− well implant 28 formed in thesecond epi layer 14. Effectively, the near reach-through 24 acts as aborder of the N− well region 28 to eliminate the lateral bipolar gain.As shown in FIG. 1, the structure further comprises shallow trenchisolation (STI) structures 30 a-30 f, N+ diffusion regions 32 a-32 c,and P+ diffusion regions 34 a and 34 b. It will be understood by one ofskill in the art that the N+ diffusion regions 32 a and 32 c form thecathode, and the P+ diffusion regions 34 a and 34 b form the anode, ofan STI-bound P+/N− well diode.

FIG. 2 shows a triple-well double-epi ESD device according to analternative embodiment of the invention. The alternative embodiment ofFIG. 2 differs from that of FIG. 1 in various ways. First, in FIG. 2 thenear sub-collector 18 and N− well 28 are not adjacent to or in contactwith the deep and near reach-throughs 22 and 24. Second, in FIG. 2, thediffusions on the surface of the device are rearranged such that in FIG.2, the P+ diffusion 34 is in the center of the device, and is surroundedby N+ diffusions 32 a-32 d. Therefore, this embodiment forms a P+/N+diode in an isolated P− region.

In the alternative embodiment of FIG. 2, the N+ diffusions 32 b and 32 cserve as the collector, while the N+ diffusions 32 a and 32 d serve asthe electrical contact to the near reach-through 24, and the nearsub-collector 18 serves as a low-resistance cathode and reducesinjection into the isolated epi region 20. The deep and nearreach-throughs 22 and 24 isolate the isolated epi region 20 such thatthe near sub-collector 18 and the isolated epi region 20 are moreisolated than in the embodiment shown in FIG. 1, and can beindependently biased. Thus, it is possible to change the capacitancebetween the near sub-collector 18 and the isolated epi region 20,independent of the substrate 10. Additionally, injection from thesubstrate 10 back into the P+/N+ diode is likewise prevented. In thisway, a string of such devices will not communicate with each other, butrather, each diode will work independently.

In the alternative embodiment of FIG. 2, the DTI 26 is optional, but ifit is not employed, then the deep and near reach-throughs 22 and 24should be three-dimensional rings. If the DTI 26 is employed and is athree-dimensional ring, then the deep and near reach-throughs 22 and 24may or may not be three-dimensional rings, and in fact, may or may notbe present.

This double-epi structure is advantageous over triple-well CMOS in thatin triple-well CMOS technology, the PFET or NFET are both not trulyisolated from the chip substrate. Rather, the PFET or NFET is located inan N− well or P− well (respectively), and the N− well or P− well isabutting the substrate, which does not completely isolate the PFET orNFET. In contrast, as will be understood from the above discussion, theembodiment of FIG. 2 will completely isolate a P-type device (e.g. aPFET) or an N-type device (e.g. an NFET) from the substrate.

FIG. 3 shows an alternative triple-well double-epi ESD device accordingto an alternative embodiment of the invention. The alternativeembodiment of FIG. 3 differs substantially from that of FIG. 2 in that asecond near reach-through structure(s) 34 a and 34 b electricallyconnect the near sub-collector 18 and the N+ diffusion(s) 32 b and 32 c.In this manner, the series resistance of the cathode is lowered. Itshould be understood that the diffusions on the surface of the devicemay alternatively be rearranged such that an N+ diffusion is in thecenter, with the second near reach-through 34 adjacent to it, andelectrically connecting it to the near sub-collector 18.

FIG. 4 shows an alternative double-epi double sub-collector polysiliconbound diode ESD device. The alternative embodiment of FIG. 4 differsfrom that of FIG. 3 in that while FIG. 3 employed an STI-bound diode,the embodiment shown in FIG. 4 employs a polysilicon bound diode. Thatis, instead of the central P+ diffusion 34 being surrounded by ST1s 30 cand 30 d as shown in FIG. 3, in FIG. 4 the central P+ diffusion 34 issurrounded by a polysilicon MOSFET gate structure 36. As will beunderstood by one of skill in the art, the polysilicon MOSFET gatestructure 36 comprises a thin film dielectric (e.g., an oxide layer), apolysilicon film, and spacer(s) on the sidewall(s). Effectively, thepolysilicon MOSFET gate structure serves as a block mask (e.g., dummystructure) to break the silicide between the P+ and N+ regions; that is,insulation which forms the spacers is used to prevent shorts.

FIG. 5 shows an alternative double-epi double sub-collector ESD devicewith an N+ diffusion 32 b as the contact to the N− well 28, connected byan optional near reach-through 34. Whereas previous embodiments employedan N− well to substrate diode, the embodiment of FIG. 5 shows an N+diffusion diode, which can discharge into the doped region 20 in thefirst epi layer 12. It will be understood by one of skill in the artthat it is not necessary that the N+ diffusion 32 b be as wide as isshown in FIG. 5, but rather could optionally be surrounded by a P+diffusion. Additionally, as another alternative, the electrodes may beswitched as discussed above with reference to FIG. 3. In any case, inthe embodiment shown in FIG. 5, when the deep sub-collector 16, and thedeep and near reach-throughs 22 and 24 are tied to V.sub.dd, a verticalNPN transistor is formed for discharge between negative pulses andV.sub.dd, that is, for negative polarity pulse events. Thus a verticalbipolar NPN transistor is formed between the deep and nearsub-collectors 16 and 18.

FIG. 6 shows an alternative double-epitaxy ESD device. In thisembodiment, an N+ diffusion diode is located in an isolated epi region20. In this embodiment, the reach-through structure 22 and 24 and thedeep sub-collector 16 form the cathode of an STI-bound diode or a PNdiode.

FIG. 7 shows an alternative double-epi triple-well diode ESD device. Inthis embodiment, a P+/P− diode is formed, and the N+ diffusion 32 b andthe deep sub-collector 16 form cathodes of two diodes in parallel.

FIG. 8 shows an alternative vertical SCR double-epi ESD device. In thisembodiment, the P+ diffusion 34 b is located in an N− well 28.Additionally, an SCR is formed by the PNPN structure produced by the P+diffusion 34 b, the N− well 28, the P− doped region 20, and the N+ deepsub-collector 16. The P+ diffusion 34 b serves as the anode, and thedeep sub-collector 16 serves as the cathode. It should be understood byone of skill in the art that the N− well 28 may or may not extend intothe first epi layer 12.

In the embodiments shown in FIGS. 2-5 and 8, the doped region 20 iseffectively isolated as though in a Faraday cage. That is, the dopedregion 20 is isolated vertically by the deep sub-collector 16, laterallyby the reach-through structures 22 and 24, and optionally by the DTI 26.In the Faraday cage, the deep sub-collector 16, and the reach-throughstructures 22 and 24 are not merged, in embodiments. The doped region 20is sometimes referred to as an “isolated epi” region.

Additionally, in these embodiments, the deep sub-collector 16 and thenear sub-collector 18 are coupled together such that the verticalinjection from the P+ diffusion regions 34 a and 34 b into the substrate10 is eliminated. Rather, because the near sub-collector 18 isphysically separated from the deep sub-collector 16, the injection is tothe doped region 20 of the first epi layer 12, which is grounded.Furthermore, the DTI 26 eliminates the lateral injection into anyadjacent structure.

As will be understood by one of skill in the art, the lower the sheetresistance of the N− well 28, the better the ESD protection. For thisreason, the parallel resistance of the deep and near sub-collectors 16and 18 provide a low-resistance cathode which effectively improves theESD protection.

It will be understood by one of skill in the art that the doped region20 in the first epi layer 12 and the deep sub-collector 16 together mayform an element of the device. In the case of a bipolar transistor,these two regions form the base and collector. In the case of a PNPNstructure, these two regions form the latter two PN elements, as in thecathode of a silicon controlled rectifier (SCR). In the case of an NPNstructure, these two regions form the PN elements.

FIG. 9 shows an alternative lateral-vertical SCR double-epi ESD device.In this embodiment, the diode is polysilicon bound rather thanSTI-bound, as discussed above in reference to FIG. 4. The diode may beeither an N-diffusion or an N− well diode. This embodiment differs,though, in that the N− well 28 is sufficiently narrow such that thepolysilicon gate structure 36 extends beyond the area between the N−well 28 and the P− region of the second epi layer 14, such that a veryhigh-current, low-voltage turn-on circuit is produced. It will beunderstood that PNPN regions are formed both vertically and laterally.The P+ diffusion region 34 forms an anode and the 16 sub-collector formsa cathode of a vertical SCR; while the P+ diffusion region 34 forms ananode and the N+ diffusion region(s) 32 b and 32 c form(s) the cathodeof a lateral SCR.

FIG. 10 shows a double-epi double sub-collector Silicon Germanium (SiGe)hetero junction bipolar transistor (HBT). In this embodiment, the devicecomprises a base structure 38 on the surface of a shallow trenchisolation 30 b. The device further comprises an emitter structure 40 incontact with the N− well 28. In embodiments, as should be well known tothose of skill in the art, the emitter structure includes N-typepolysilicon (which forms the emitter) formed between insulators on alayer of single crystal silicon germanium. In this embodiment, the nearsub-collector 18 is in contact with the deep sub-collector 16.

FIG. 11 shows a double-epi double sub-collector Silicon Germanium (SiGe)hetero junction bipolar transistor (HBT) with ring isolation. In thisembodiment, the device comprises a base structure 38 on the surface of ashallow trench isolation 30 b. The device further comprises an emitterstructure 40 in contact with the N− well 28. In this embodiment, thenear sub-collector 18 is in contact with the doped region 20, which is,in turn, in contact with the deep sub-collector 16.

In the double-epi triple-well embodiments discussed above, the P− regionin the first epi layer may be an isolated epi region, which is boundedby the deep and near reach-throughs and the deep sub-collector. In theseembodiments, the deep and near reach-throughs and the deep sub-collectorisolate the first epi layer and serve as a cathode, or serve as anindependent electrode.

In all the embodiments discussed above, the structure and arrangement ofthe dual epitaxial layers and alternative elements protect against thedamage cause by ESD, and yet decrease the injection from the P+ or N+diffusion into the substrate, such that noise is reduced. Additionally,in the various embodiments, benefits can be realized, for example:reduction of the lateral bipolar gain; elimination of the lateralinjection to adjacent structures; independent biasing of an isolated epiregion; prevention of injection from the substrate back into the device;preclusion of Darlington string amplification effects; production of avery high-current, low-voltage turn-on circuit; or complete isolation ofa P-shape or an N-shape from the substrate, all while maintaining theability to discharge surges in voltage.

The circuit as described above is part of the design for an integratedcircuit chip. The chip design is created in a graphical computerprogramming language, and stored in a computer storage medium (such as adisk, tape, physical hard drive, or virtual hard drive such as in astorage access network). If the designer does not fabricate chips or thephotolithographic masks used to fabricate chips, the designer transmitsthe resulting design by physical means (e.g., by providing a copy of thestorage medium storing the design) or electronically (e.g., through theInternet) to such entities, directly or indirectly. The stored design isthen converted into the appropriate format (e.g., GDSII) for thefabrication of photolithographic masks, which typically include multiplecopies of the chip design in question that are to be formed on a wafer.The photolithographic masks are utilized to define areas of the wafer(and/or the layers thereon) to be etched or otherwise processed.

The resulting integrated circuit chips can be distributed by thefabricator in raw wafer form (that is, as a single wafer that hasmultiple unpackaged chips), as a bare die, or in a packaged form. In thelatter case the chip is mounted in a single chip package (such as aplastic carrier, with leads that are affixed to a motherboard or otherhigher level carrier) or in a multichip package (such as a ceramiccarrier that has either or both surface interconnections or buriedinterconnections). In any case the chip is then integrated with otherchips, discrete circuit elements, and/or other signal processing devicesas part of either (a) an intermediate product, such as a motherboard, or(b) an end product. The end product can be any product that includesintegrated circuit chips, ranging from toys and other low-endapplications to advanced computer products having a display, a keyboardor other input device, and a central processor.

While the invention has been described in terms of embodiments, thoseskilled in the art will recognize that the invention can be practicedwith modifications and in the spirit and scope of the appended claims.

1. A device comprising: a P− doped region located within a firstepitaxial layer; a sub-collector formed in an upper portion of asubstrate and a lower portion of the first epitaxial layer; areach-through structure connecting the sub-collector and a first N+diffusion region; a second N+ diffusion region diffused in the secondepitaxial layer; and a P+ diffusion region diffused in the secondepitaxial layer and isolated from the N+ diffusion regions.
 2. Thedevice of claim 1, wherein the isolation is shallow trench isolationstructures which further isolate the first and second N+ diffusionregions and the P− doped region located within a first epitaxial layerwhich is isolated by a deep trench isolation structure.
 3. The device ofclaim 1, further comprising a polysilicon MOSFET gate structure betweenthe second N+ diffusion region and the P+ diffusion region forming apolysilicon bound diode.
 4. The device of claim 3, wherein: the P+diffusion region forms an anode and the sub-collector forms a cathode ofa vertical silicon controlled rectifier; and the P+ diffusion regionforms an anode and the N+ diffusion region forms the cathode of alateral silicon controlled rectifier.
 5. The device of claim 1, whereinthe reach-through structure and the sub-collector form a cathode of anN+ diffusion diode.
 6. The device of claim 1, wherein the sub-collectorforms a cathode of a P+/P− diode and the second N+ diffusion regionforms the cathode of an STI-bound PN diode.
 7. The device of claim 1,wherein the P+ region forms an anode and the sub-collector forms acathode of a vertical silicon controlled rectifier.